For the RTP and ABP models, we do not have exact expressions for \(p_{ac}\) , but we can get such an expression for
the AUOP model, where the distribution \(p_{ac}\)  is a Gaussian due to linear drift in the Kramers equation
[1]}. Since we know the variance \(\langle v^2\rangle _{ac}\)  from Eq. (REF ), we infer
\(p_{ac} (v) \propto e^{-\frac{\tau + \tau _r + \tau ^2\mu K}{D_f} \frac{v^2}{2}}, ~~~~~~ \text{AOUP}.\) 
